The X-37B (pictured) one of two in the Air Force fleet, conducted unspecified experiments for more than 700 days while in orbit. The upcoming mission – known as Orbital Test Vehicle-5 – is lifting off from Launch Complex 39A at Nasa’s Kennedy Space Centre in Florida

ORBITAL TEST VEHICLE-5

The upcoming mission – known as Orbital Test Vehicle-5 – is lifting off from Launch Complex 39A at Nasa’s Kennedy Space Centre in Florida.

This is the first time a space plane has launched on a Falcon 9 rocket – with the previous four being launching on the Atlas V rockets.

The US Air Force’s unmanned X-37B space plane has flown three previous secret missions to date.

Each time it has carried a mystery payload on long-duration flights in Earth orbit.

Media reports suggest the liftoff will take place early in September.

SpaceX´s first publicly disclosed launch contract for the Air Force was awarded last year for a next-generation Global Positioning System satellite flight in 2018.

‘The many firsts on this mission make the upcoming OTV launch a milestone for the program,’ said Randy Walden, the director of the Air Force Rapid Capabilities Office.

‘It is our goal to continue advancing the X-37B OTV so it can more fully support the growing space community.’

The secret military spacecraft is set to launch from Kennedy Space Center’s Pad 39A on the morning of September 7 according to nasaspaceflight.com

SpaceX last week conducted a Static Fire test on the Falcon 9 rocket to be used, a key milestone ahead of the rocket’s first launch of a U.S. Air Force X-37B spaceplane for the OTV-5 mission.

Four previous X-37B missions have been launched by United Launch Alliance Atlas 5 rockets.

The US Air Force’s unmanned X-37B space plane has flown three previous secret missions to date.

Each time it has carried a mystery payload on long-duration flights in Earth orbit.

According to the Air Force, one on board OTV-5 payload is US thermal spreader which will test the longevity of electronics and heat pipes in the space environment.

‘The fifth OTV mission continues to advance the X-37B’s performance and flexibility as a space technology demonstrator and host platform for experimental payloads,’ it said.

‘Building upon the fourth mission and previous collaboration with experiment partners, this mission will host the Air Force Research Laboratory Advanced Structurally Embedded Thermal Spreader payload to test experimental electronics and oscillating heat pipe technologies in the long duration space environment.’

SpaceX´s first publicly disclosed launch contract for the Air Force was awarded last year for a next-generation Global Positioning System satellite flight in 2018.

A second GPS launch contract was awarded in March.

The contracts are valued at £83 million ($65 million) and £96.5 million ($75 million), respectively.

In May 2016, the US National Reconnaissance Office disclosed it had hired SpaceX to launch a spy satellite aboard a Falcon 9.

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The reusable X-37B Orbital Test Vehicle (pictured) returned in June, concluding an almost two-year mission in orbit, according to the US Air Force

The mission, which was arranged through an intermediary, Ball Aerospace, took place in May.

In June this year the unmanned military space plane landed at Kennedy Space Centre Sunday with a sonic boom concluding an almost two-year mission in orbit, according to the US Air Force.

The Air Force tweeted shortly after 8am that the vehicle had landed safely, marking the conclusion of its fourth classified mission, which lasted more than 700 days.

The unmanned X-37B, which resembles a mini space shuttle, landing on a runway used by the now-mothballed craft.

The Boeing-built space plane blasted off in May 2015 from nearby Cape Canaveral Air Force Station aboard an Atlas 5 rocket built by United Launch Alliance, a partnership between Lockheed Martin Corp and Boeing Co.

The X-37B, one of two in the Air Force fleet, conducted unspecified experiments for more than 700 days while in orbit.

It was the fourth and lengthiest mission so far for the secretive program, managed by the Air Force Rapid Capabilities Office.

The Air Force said the orbiters ‘perform risk reduction, experimentation and concept-of-operations development for reusable space vehicle technologies.’

The Air Force tweeted that the vehicle had landed safely, marking the conclusion of its fourth classified mission, which lasted more than 700 days

However, the exact nature of the mission and its cost is classified.

The Secure World Foundation, a nonprofit group promoting the peaceful exploration of space, says the secrecy surrounding the X-37B suggests the presence of intelligence-related hardware being tested or evaluated aboard the craft.

The vehicles are 29 feet long and have a wingspan of 15 feet, making them about one quarter of the size of the National Aeronautics and Space Administration’s now-retired space shuttles.

The X-37B, also known as Orbital Test Vehicle, or OTV, first flew in April 2010 and returned after eight months.

A second mission launched in March 2011 and lasted 15 months, while a third took flight in December 2012 and returned after 22 months.